Previous sections have described the establishment of clear and logical processes for conducting road and highway planning. This section describes analysis tools and methods that are used to inform the various steps of the planning process. These tools and methods support planning efforts at all levels including system, corridor, and project planning. Established procedures to collect, manage, and analyze data are critical in identifying road and highway needs; evaluating the benefits and costs of potential projects; and comparing the effects of various projects and programming decisions.

Another important type of system performance data is crash locations and characteristics. Key crash characteristics include the location, time, and environmental conditions of the crash; vehicles and persons involved; nature and extent of injuries and property damage; and contributing factors. Crash reporting practices vary both at a national and local level. If local or national databases do not exist, interviews with public and private transport operators, local transport officials, or law enforcement officials can help pinpoint frequent locations of crashes and other incidents. Safety councils of the police, highway department, and other agencies, established to coordinate accident response procedures, may also serve as a source of data. Click here to see an example of a national and regional crash data reporting system.

Information on the location and severity of crashes can be used to identify and prioritize facilities for safety-related improvements. Information on conditions, contributing factors and outcomes is also valuable in assessing the effectiveness of various actions to improve safety. Data on crash frequency by location should be used in conjunction with measures of exposure (for example, traffic volumes) to assess relative hazards and prioritize locations for improvement.

In addition to increasing overall traffic, transport investments may affect the distribution of existing traffic by changing the relative cost of travel on various transport routes.

Demand forecasting involves a set of analytical procedures to estimate future levels of transport system use as a result of changes in population characteristics, economic activity, and transport network conditions, and of subsequent changes in travel patterns. Demand forecasting serves different purposes depending upon the level of the study. For strategic planning, forecasts are needed to evaluate the overall viability of alternative strategies and the demand for individual components of these strategies. For corridor planning, forecasts are needed to determine the adequacy of existing facilities and services in the corridor and the potential need for expanding these facilities and services. For facility planning, forecasts are needed to determine the appropriate capacity of new facilities that may be built and of existing facilities that are being considered for expansion.

Methods for demand forecasting can range from very simple to very complex. At the most basic level, past trends in traffic growth can be extrapolated to predict future levels of traffic in any given year. A more sophisticated approach will estimate future traffic based on projections of the underlying drivers of traffic - for example population, economic activity, vehicle ownership. Either of these methods can be applied at a regional or corridor level to provide a rough estimate of future transportation demands. More sophisticated methods of forecasting the underlying variables are likely to result in more accurate traffic forecasts.

The population and employment forecasts provide a basis for estimating future "background" flows on the system. The future transportation network can then be varied to describe proposed improvements to the road and highway system. This will predict the changes in the distribution of future traffic over the network, and to some extent will predict increases in travel caused by reductions in transportation costs. Demand forecasting methods have primarily been developed for urban applications, but these same methods are increasingly being adapted for state or regional planning. See the following references for additional information on demand forecasting:

A World Bank study group is also looking at advanced travel forecasting models and their potential application to regional road and highway planning.

Various surveys and counts must be performed to support travel demand forecasting using four-step or other network-type models. Basic data requirements include:

Household travel surveys, which ask people to record their trip patterns (origin, destination, mode, purpose, time, etc.) over a fixed time period. These are used to establish existing travel patterns and as a basis for modeling responses to future system changes.

External or cordon surveys, which are performed at the boundary of the study area to identify trips for which one or both ends are outside the area.

Traffic counts, which are used to calibrate models (for example,, compare actual to predicted flows and adjust model coefficients to improve accuracy.)

See Items 5 and 6 in the "Selected References" section of this document to read about other types of surveys, such as employer-based surveys and transit on-board surveys, which may also be used to support modeling. Click here to display or download the Travel Survey Manual prepared by Cambridge Systematic, Inc. for the U.S. Department of Transportation, Federal Transit Administration, Federal Highway Administration, Office of the Secretary, and the U.S. Environmental Protection Agency (July 1996), which contains a detailed description of the various types of travel surveys and how to implement them, and also to view samples of different types of travel surveys.

Demand forecasting models originally focused on personal travel, but recently the importance of forecasting freight and other commercial vehicle traffic has received increasing attention. A noteworthy difference between freight and passenger travel analysis is that in the case of freight analysis, interviews with logistics coordinators at a sample of larger businesses and freight shipping companies can often provide a good picture of the primary freight travel patterns and needs. Passenger travel patterns, in contrast, vary at the level of the individual and random, large-sample surveys of the population are required.

System-level cost estimation is a useful technique for regional road and highway planning. System-level cost estimation uses local project cost experience as the basis for cost estimates of candidate projects and programs. It is primarily useful for long-range planning efforts, in which financially constrained system plans are required but information is not sufficient to estimate detailed quantities and unit costs.

Operating and maintenance cost estimating for road and highway systems generally includes labor, materials, and supplies expenditures that are consumed in operating the system over a given time period, usually a year.

Life cycle costing is an economic assessment of all significant costs of ownership of an asset over its economic life, expressed in equivalent dollars. Life cycle costing requires information on the capital cost of the project, its useful life, and annual O&M costs. Costs are then discounted over the lifetime of the project using an appropriate discount rate. Life cycle costing can assist in setting design and construction standards to minimize total costs over the project lifetime. For example, use of more durable pavement increases construction costs but decreases O&M costs over the project lifetime.

Established methods and software are available to analyze these tradeoffs; see the following references:

Environmental impacts include air quality, water quality, habitat destruction and fragmentation, noise, and greenhouse gas emissions. The impacts of a road or highway project on water quality and habitat are frequently negative but can be mitigated to some extent through appropriate design and construction techniques. Click here for more information on environmental mitigation of roadway projects. Air quality, greenhouse gas, and noise impacts, which result from vehicle operations, also may be negative as a result of increased traffic on the roadway. These can be mitigated most effectively through regulation of vehicle technology, including emissions controls, fuel efficiency standards, and noise standards. They can also be mitigated through provision of high-quality service by alternative, less environmentally damaging modes of transport such as public transportation, railroad, and non-motorized transport.

Other impacts may include factors such as the social impacts on a community of a new road or highway project. For example, construction of a highway may improve the delivery of services to a rural village but may also bring about community changes due to increased traffic. Where a project will significantly impact a community, a qualitative assessment of the nature of these impacts should be considered in assessing the benefits and costs of the project.

In addition to examining total impacts it is also important to examine the distribution of impacts (for example, who benefits and who is negatively impacted.) Assuring an equitable distribution of benefits may be important from a local or national policy standpoint. Geographic equity is one aspect, e.g., ensuring that all regions of a country benefit from road and highway investments, and that rural as well as urban areas benefit. Equity among social classes may also be important, e.g., it may be important to ensure that economic opportunities reach those for whom existing conditions are poor. Mechanisms for funding roads should also be fair in the sense that those who are financing the project are also those who are benefiting from the road improvements.

Manual of Transportation Engineering Studies. 1994. Institute of Transportation Engineers. H. Douglas Robertson, ed. Available at the ITE On-line Bookstore. Item TB-012. Use document title as the search criteria.

AASHTO Guidelines for Traffic Data Programs. 1992. American Association of State Highway and Transportation Officials. Available at the ITE On-line Bookstore. Item LP-329. Use document title as the search criteria.

Markow, M.J. et al. 1994. Role of Highway Maintenance in Integrated Management Systems. National Cooperative Highway Research Program (NCHRP), Report 263, National Academy Press, Washington, DC. Available at the Transportation Research Board on-line Bookstore. Book Code: NR363, ISBN: 0-309-05361-7.